Multiple effect evaporator



NOV. 5, 1935. MOORE MULTIPLE EFFEC EVAPORATOR Filed Jan. 5, 1952 eSheets-Sheet I n 2 I f A 6 Sheets-Sheet 2' H. K. MOORE MULTIPLE EFFECTEVAPOBATOR Filed Jan. 5, 1952 N if Nov. 5, 1935.

Nov.

5, 1.935. H; K. MOORE MULTIPLE EFFECT EVAPORATOR Filed Jan. 5, 1952 6Sheets-Sheet 3 H. K. MOORE MULTIPLE EFFECT EVAPORATOR Nov. 5, 1935.

1932 6 Sheets-Sheet 4 7 Filed Jan. 5,

NOV. 5, 1 935. Q I K MQQRE 2,020,038

MULTIPLE EFFECT EVAFORATQR v Filed'Jan. 5, 1932 6 Sheets-Sheet 5 jaw???Nov. 5, 1935.

H. K.' Moo'RE:

MULTIPLE EFFECT EVARORATQ/R Filed Jan.- '5, 1932 e Sheets-Sheet 6- 5scribed are generally applicable tothe evapora- Patented N5v."5',"-

PATENT omce MULTIPLE mac's svarona'roa Hugh 1:. Moore, Berlin, N. 11.,minor to Brown Berlin,

Company, J N. Maine 1 11., a oorporatiqn oi Application January '5'.1932, Serial No. mass This invention relates'to apparatus forevaporating water efficiently from dilute liquors initially containing alarge proportion of watch, While the principles of the apparatus hereindetion of aqueous liquors, the evaporator is more especially designedfor the eflicient evaporation or water irom liquors such as theblackliquor from the sulphate process of digesting wood chips, such liquorbecoming viscous and tacky when a considerable proportion of the wateris removed therefrom. The present inventiongrelates more especially tothe evaporation 01' water from liquors 5 containing substances which areliable twcause troublesome scale within the evaporator, this beingtrueof the black liquor from the sulphate process. The multiple-effectevaporator herein described is in general similar to that described andillustrated in my Patent No. 1,582,067, but includes a number ofimproved features which have been incorporated for the purpose of over-1 coming certain difflculties whichhave been extors in the evaporationof black liquorirom sul- 25 perienced'in the operation often-eflect'evaporaphate cooks.

The black liquorwhich is discharged from adigester after a sulphate cookcontains a large number of substances including various lignin compoundsand the sulphates and. carbonates or sodium and calcium. .The primaryurpose or the evaporator is to concentrate the black liquor by removal tas much as possible of its aqueous content so that the ,lignin compoundswhich inbeing. an endothermic reaction elude roughly 43 per cent oiinorganic mattrand 5'7 per cent of organic matter can be calcined withthe addition of salt cake to produce soda ash and sodium sulphide. Theformer is subsequently cau'sticized by the addition of lime to formcaustic soda.v It, is desirable that as much as possible of thesalt-cake be reduced to sodium sulphide in the urnace according to theequation 5 i depending on the temperature for its degree of completion.u

' Hence it is desirable? that the temperature. oi the furnace hm hish aspossible. The temperature: 1

-- of. the furnace, in turn, depends onthe concen- 1 tration of theblack liquor supplied thereto, since the-more heat required forthebvaporationoi the remaining aqueouscontent oi the concentrated blackliquol', the less heat will beleitirom' the combustion of the liquor topromote the r'e- I duction of the salt cake. For thisreaeon. the de-.gree oi concentration of the black liquor delivered oi the "presentinvention to provide apparatus 21 (Jllllll. 159-1 i" from the evaporatorto the furnace determines in large measure the emciency oi the entirecycle or operations'eonstituting what is known as the sul-' phateprocess of. pulp digestion. It is an object which is capable ofconcentrating black liquor to a considerably higher degree than hasheretotore been practically possible, this being accomplished, accordingto the present invention with less clcggingoi the-evaporator thanhas'hereto- 10 fore been encountered-in. the operation of. evaporatorsotthis type. Moreover, according to the present invention, variousadditional economies areeflected as hereinafter more iullyset forth.

Multiple eflect evaporators consist of a number of separate units oreffects which, operate in a series or descending. temperatures andpressures. Steam at maximum pressure is introduced into the end efl'ectusually designated as #l to boil liquogcontained in this efle'ct. Thesteam boiled 2 out from the liquor is carried to #2 eflectat a lowertemperature and pressure to boil-liquor therein which is at a stilllower temperature. The steam generated from the liquor in #2 effect ispassed to #3 eflect, and so on, down the line until the steam from #IO'effect (in a ten-effect evaporator) is carried ofl to-a condenserin-Jw'hich is preferably maintained a high vacuum -in order that theboiling point in the lasteflect may be as low'as possible. The course ofthe liquor through the evaporator may be from #I through thesuc- Icessively cooler eil'ects to #IIL In such case, it is thick and tackyat'the usual. operating tempera-- ture of elect-the degreeii-concentration to which the liquor may b'e'evaporated' in this way 5 tis greatly Instead'oisending the liquor through theeflects in successionfrom l' to #10, the direction or flow ofthe liquormay be reversed,

* the weakliquor bcinilzi troduced into #1. effect to #1 This his-theadvantage otdelivering' the centration is poesible'owi'ng to the reducedviseosityor the concentrated liquor in its heated 55.-

I condition. The weak liquor which is supplied to the'evaporator is,however, ordinarily at a fairly high temperature, considerably abovethat of I ll effect. Hence if hot liquor is sent through the evaporatorin reverse direction, that is, from #it through the successive effectsto #l, a great deal of this initial heat is lost when the liquor enters#Iil effect. As set forth in my Patent N 0. 1,582,-

067, I prefer to-introduce the weak liquor into an intermediateeifect,as for example, #5. From this effect. it is sent through progressivelycooler effects, #6, #1, #a, #9, and In. The liquor fr'om '#IB is thensent through progressively hotter the storage tank is brought intoheat-exchanging relationship with the cold, partially concentratedliquor from #lil effect before it is introduced into I the evaporator sothat the excess heat in the weak introduction into #5 effect.

liquor is utilized to raise the temperature of' the cold liquor from#lil, this partial cooling of the initially hot liquor supplied from thestorage tank being additionally desirable sinoe it reduces thetemperature to a point suitable for economical The incidental advantagesarising from this manner. of circulating the liquor through theevaporator are discussed in full in my patent hereinbefore referred to.

When the liquor progressing through a teneffeot evaporator reaches thelast two or three stages of evaporation, it becomes increasingly dimcultto handle due to its physical characteristics arising from the highconcentration of solids therein. Black liquor contains a certain amountof calcium sulphate which, in the weak liquor, is largely, if notwholly,in solution. As the liquor becomes more concentrated, anincreasing amount of calcium sulphate is forced out of solution. Theprecipitate at first takes the hydrated form of C8.S04.2H2O. This is-asoft compound and is not of itself-troublesome. However, if exposed toheated surfaces such as the tubes in the hotter effects through whichthe liquor passes, the soft hydrated form of the calcium sulphate losesits water of hydration and changes to anhydrous calcium sulphate,asfollows:

This anhydrous form of the sulphate, known as anhydrite, is a hardglassy mineral. When a substantial layer of this mineral is formed onthe inner surface of evaporator tubes, its low heatconducting propertiesgreatly reduce the efliciencyv of the evaporator and the eflectivediameter of the tubes so that it is necessary from time to time toremove this scale from the tubes. 1 In the saltmaking industry, suchscale is frequently encountered on the exterior surfaces of theevaporator pipes. It can be removed in such cases by being broken upwith a sledge hammer. When the scale forms on the interior surface oftubes, the problem of its removal is far more .diiilcult. Variousmethods of removalhave been triedsuch as rotating burrs to bore thescale out of the tube.

This is extremely difiicult owing to the glass-like the tubes to crackup the scale, the tubes themthis method works well with pure anhydrite,it a not so successful with anhydrite deposited from black liquor. Thisis due to the presence of a considerable quantity of extremely finefiber material from the pulp, this material being so fine 5 that it ispractically impossible to remove it from the black liquor. Cellulosicfibers are slightly denser than water and therefore tend to settle. Theeffective density of the fine fibrous material in the black liquor whenit reaches a fairly con- 0 centrated stage, is greatly increased by thefact that owing to the concentration of the liquor, an increasing amountof sodium sulphate is forced out of solution, the minute crystals ofthis sulphate attaching themselves to the fibers. This 15 causes thesettling of the fibrous material in horizontal evaporator tubes so thatas anhydrite scale is formed, a considerable amount of fiber is caughttherein. This makes the scale tougher-and less brittle. The presence ofthe fiber also practically 20 prevents washing. of the scale from thetubes, in spite of the ready solubility of the sodium sulphate. Whenwash water is sent through the tubes, the first layer of mineral washedfrom the surface of the scale exposes a fuzz of fiber which 25 acts as ablanket to prevent effective access of wash water: to the remainingscale. According to the present invention, these difllculties are easilyaccessible for replacement or repair and 40,

that they be of such size and shape as not to interfere with thecirculation of liquor in the effect. Furthermore, the structure shouldbe such as to ensure the eiilcient removal from the scraper of thesolids which are scraped from the surfaces of 5 the tubes. The use ofvertical tube effects for the last two stages of evaporation isadvantageous in that such structure lends itself more conveniently tothe use of reciprocating scrapers within the tubes, and thus there isless tendency 50 on the part of the fibrous material which is laden withsodium sulphate crystals to settle out against the wall of the tubes. Bythe use of scraping devices such as are hereinafter moreparticularlydescribed, not only is it possible to deliver the 55 concentrated blackliquor at a considerably higher degree of concentration than hasheretofore been possible, but the evaporator as a whole can be run forlonger periods between washings.

The invention also includes various improved 0 features of structurewhich combine to make possible the operation of an evaporator of thistype at a much higher efiiciency than has been heretofore possible. Inthe horizontal effects, it is necessary formaximum efiiciency to keepthe en- 5 tire area of the inner surfaces of the tubes wet at all timeswith liquor. In ,the effects through which the relatively weak liquor ispassed, the volume of such liquor is ordinarily suflicient of itself tokeep the tubes full of liquor and its foam. 70 As the liquor'becomesmore and more concentrated after successive steps of evaporation, thestream eventually is not sufficient to wet the entire inner surface ofthe tubes. For this reason,

I have heretofore re-circulated a. portion of the 75 aus- " 'mentthesize 01' the stream actually passing through; the tubes and thus to keepthe tubes suiilciently full. This, however, is objectionable since there-ci'rculated liquor is more conc'en-' trated than the-liquor enteringthe eflect so that the-boiling point is alteredv and the efliciencyoithe eiiect is somewhat decreased. According to the present invention, Iprovide dams outsidepi the discharge ends of the tubesso'that a certainamount of iiquorjcan back .up in the-tubes to flil the same sufiicientlywithout necessitating a recirculation of a portion of the liquortherein.

tor, pumps are essential for the circulation of the liquor through thesuccessive eiiects. Since the.

liquor from each efiect is discharged therefrom immediately after havingbeen boiled by the steam surrounding the tubes through which it haspassed, the liquor fromv each effect thus reaches thecorresponding-pumpat a tempera- This. heat raises the temperature of the incoming liquor.so that the latter boils ,sufliciently to flllthe pump with steam. Thisrenders the pump ineflective. The expedient of placing the pumps at thebottom of deep pi s about thirty feet below the effects has been triedwith more or'less success. When in the pits, however, the pumps usuallytail to receive the attention and care which they require. According.tothe present invention, the steam within each pump'is condensed so asto-permit the pump to operate efiectively. It is impracticable toattempt to cool the pump itself from the outside. It is likewiseundesirable to inject cold water into the pumps since the water thusintroduced will have. to be evapo-. rated. According to the invention, Iintroduce into each pump cold liquor from evaporator.

This liquor, although partially concentrated, contains a.considerable-percentage oiwater, but as I this water has to beevaporated anyway, no loss .of e iiiciency results from its introductioninto the several. pumps. ,Special structure by which the cold liquor isintroduced into the pumps eiilciently, is hereinafter described.

In 'a multiple effect evaporatorhaving horizontal eiiects, it isadvantageous to distribute the .liquor in each eiiect as evenlyaspossible among.

thetubesin each row. The nozzles described and illustrated in thepatents referred to to operate on i its aoaopss ruptedand the core ofliquor goes through as a 3 over the area of the tube plate. It has beenfound in practice that nozzles i this type work satis- -i'actorily uptoa out et. 'It seems impossible to make nozzles larger than thatwilleither have the required angle of discharge or that will 5. give auniform spray under varying pressures.

. core and is not transferred to the interior of the In the operation ofa multiple eflect evaporacore. At lower velocities, thecore is notdisstraight stream. On the other hand, at higher pressures, the corewill be disrupted to such an extent that you will obtain a hollow conewhich is .the very thing toavoid as it does not get equal distributionover 'the tubes. In other words, a

large nozzle is capable oi'iurnishing a suitable cone of spray only at agiven pressure, Slight variations either'above orbelow such pressure reasuit either in o. spray with a solid stream in the center and vacantspaces around it, or in a hollow cone with no stream in the center. Itis a practical impossibility to supply liquor to the severalefiects atanything like uniform pressures. ,I-Ience the nozzle must be capable ofefiicient distribution over a considerable range of pressures. It isalso desirable that nozzles be capable of operating properly withliquors of difierent viscosities. In order to fulfill these conditions,it is necessary to use small sized nozzles. If a singlenozzle isincapable of taking care ofihe entire stream by a plurality of nozzlesmay notbe theoretically 40 as uniform as a single nozzle, the gillflanges'assist in attaining reasonable uniiormityof distribution. Thereis one characteristic of small nozzles which has to be considered,namely, the

fact that dueto resistance in the nozzles themselves, an increase inpressure inthe liquor suppliedthereto does not result in a correspondingincrease in the volume of liquor passing through the nozzle. In tact,the point can be reached where very little increase in volume may beobtained for a tremendous increase in pressure. It

sometimes happens in mill operation that for sonie reason connected withother parts :of a plant, the capacity of the evaporator has, to beincreased suddenly. This can be done either by increase in size of thenozzlesor increasing the number. of nozzles in each eilfect. It is outoi the question as a practical matter to change the size oi the nozzlessince that would mean coolingthe entire evaporator so as to permitaccess to the interior of each eiiect for the replacement oi'th e'nozzles by larger or smaller ones; Cons'equently, according to thepresent invention,'

two or more separate batteries of nozzles are installed in each eflect,each battery consisting of a set'of nozzles arranged to providesubstantially I nozzles be somewhat smaller than the upper noz 7 5,

a vertical exchanger sixty feet high in which the liquor to be cooled isentered at the top and flows to the bottom, the liquor to be heatedentering at the bottom and flowing out at the top. While it isconceivable that a sixty-foot exchanger might be constructed with pipesin single sections of .that length, it is better to construct theexchanger insections having pipes not over twenty feet in length.According to the invention, a heat exchanger is provided, as hereinafter.described, in which three twenty-foot sections are joined together insuch a manner as to form a substantially unitary sixty-foot exchanger,the design being such as to promote eilicient circulation of one streamof liquor through the tubes and the other stream of liquor in the spacearound and between the tubes, and to minimize the possibility ofclogging.

Owing to any one of a number of causes, such as variations in steampressure supplied to the evaporator, variation in the concentration ortemperature of the weak liquor supplied from the storage tank,orvariation in the voltage supplied to the motors which drive thecirculating pumps used for the evaporator, the apparatus as a whole mustas a practical matter work under the conditions which vary from time totime. It therefore becomes necessary to regulate the rate of delivery ofliquor from one effect to the next in such a manner that undueaccumulation, or the reverse, in any particular effect is avoided. For

changes, of considerable magnitude in the size of the liquor streamsdelivered from each effect to the next succeeding eil'ect such as wouldresult from a considerable change in the rate of supply of weak liquorto the evaporator, hand-operable gate valves are supplied in the liquorlines connectingthe'several successive eiIects. .The volume of. theliquor streams are, however, subject to small incidental variations forvarious causes. In order to take care-of such minor fluctuations, Iprovide automaticcontrolmeans for regulating the rate of discharge ofliquor from each effect to the next. To this end, I provide a by-passaround each delivery pump, this by-pass having therein an automaticvalve adapted to modify the eflective delivery rate of the pump, ashereinafter described in detail.

The primary. purpose of the entire evaporating apparatus is to recoverthe chemicals present in the weak liquor and to remove by evaporationthe water in which the chemicals are carried in solution or otherwise.Hence it is desirable that the condensate from the several effects andfrom the main condenser to which the steam'from #IO eifect is delivered,should be pure water. In order to provide means'for keeping track of theaction of the -evaporator in this respect, I pro- .vide aweir, ashereinafter described, which is designed not onlyto measure thequantityof steam delivered from the evaporator but also to indicate ,visuallythe purity of the condensate. This is accomplished .by means of asuitably placed sight glass mounted on the side oi the weir in 22!.inches vacuum. If the barometer reads 29 such a manner that a portion ofthe stream 01' condensate flows therethrough so that if the condensateis contaminated by any liquor, it is colored thereby and the result-isclearly visible. This feature is of practical importance in millpractice since the average operator works by rule of thumb more thanfrom actual knowledge of what is. going on inside of the apparatus.Suppose, for example, theoperator is told to carry inches, "thecondenser will be operated at one inch absolute pressure, but if the,barometer stands at 30 inches, the condenser will be operating at twoinches absolute pressure. The volume ofone pound of steam at one inchabsolute is nearly twice the volume of the same quantity of steam at twoinches absolute, so that the velocity of the stream of steam flowingfrom #ill effect to the condenser is proportionately greater when theapparatus is operated to maintain only one 20 inch absolute pressurein-the condenser than it is when the apparatus is operated to maintaintwoinches absolute pressure.

As the condenser pressure affects the pressures in the several effects,a decrease in'condenser pressure means increased velocity of the steamdischarged from the eflfects all along the line. This increased velocitydue to the lowered pressure may result in the entraining' of droplets ofliquor in the swiftly flowing streams .of steam. If' liquor is thuscarried into the next eflect or into the condenser, it discolors thecondensate delivered to the weir and hence acts as a warning to theoperator to reduce the vacuum. Although reduction of vacuum. in thecondenser is .an eifective way or preventing escape of liquor with thecondensate, it is undesirable as a permanent remedy as it lowers thethermal 'efllciency of the evaporator as a whole. If trouble is had withentrainment of liquor in the steam, it is better to enlarge 40 the steampipes from the=eifects in order to reduce the velocity of the steam.Furthermore,

according to the'present invention, I provide structure within eacheflect designed for more efllcient separation of liquor from; the steambe- 5 fore' the latter leaves the eil'ect. This reduces the minimumsizes of the steam discharge pipes consistent with a clear condensateand a low pressure in the condenser. Such structure is hereinafterdescribed.

In handling the condensate from different effects, float valves havebeen used to regulate the rate at which the water was sucked from oneeffect to the next by the pressure drops between the eifects. Thesefloats operate valves which let the water go through, but which preventthe steam from passing froni'one effect to the next. Inwashing out theevaporator, a fine mudlike pulp tended to collect in these valves sothat occasionally the plant .would have to be shut down so in order toclean out the valves since the accumulation of sediment hinderedthevalves from closing properly. According to the present invention, Iprovide traps in the-form of wells which are sumciently deep to requireno'valves '55 therein. In the apparatus hereinafter described, thepressure differences between most of the ef-' Iects are so small that awell having a depth of eight" to ten feet is sufhcient 'to prevent thesteam from one eifect blowing over into the next through 7 the trap. Inthe first two effects, however, the differences of steam pressure areconsiderably greater so that regulating valves are employed" between thefirst three 'eifectsinst'ead of the wells.

Forthis purpose, I employ butterfly valves which 4 s,oao,-o as are lessliable to clog the balanced valves of thisheat in connection with theoperation of the'evapofator. For the eflicient operation of theevaporator as described, it isadvantageous to introduce the weak liquorat acompa'ratively scraper elements for '45 high temperature. Thus theweak liquor in the storage tank shouldbe maintained as hotas possible.In order to keep up or to raise the tem-' perature of the liquor in thestorage tank, I may provide a condenser suitable slzeadjacent totheltank, the condenser being connected with the tank itself atdiil'erent levels. Into this condens-. er, I discharge any wastesteamwhich may be available from any part of :the mill, especially fromthe blow pits. These'intermitt'ent discharges of steam are thus utilizedto heat the liquor which is allowed to circulatefrom the storage tankthrough'the condenser. This results'in a considerable economy in theoperation of a mill.

For a more complete understanding of the in vention, reference may behad to the descrip-v tion which follows, and tc the drawings, of which:-

Figure 1 is a side elevation of a multiple ef= fect evaporator embodyingthe invention.

Figure 2 is a'plan view of the same..- Figure 3 is an elevation, showingthe horizontal effects in section, and illustrating the piping systemsfor condensate and air. 5

Figure'e is :a sectional view of oneoi the vertical eife'cts taken on avertical planer Figure 5 is a section'on the line 5-5 of Figure 4:.

Figure 6 is a section on the line l-Bioij'ig ure4.- Figure .7 is asectional. view or one of the in Figure 4.

- of the horizontal eflects'.

K Figure 10 is a section on the line iii-x-lll of Figure 9.

Figure 11 is a sectionflsimilar to showing only one set-of nozzles.Figure 12 is a fragmentary end elevation ofthe tube sheet in ahorizontal eiiect atthe supply ends 01 the tubes.

Figure 13 is a section on Figure 12. Y

Figure 14 is a'fragme'ntary section similar to tFigure 13, but showingthe discharge ended! the u es. i V

Figure 15 is similar to Figure 14, butshows a modified structure. Figure16 is 'a'section on the line iB- -it of Figure 9.

Figure 1'? is a section onthe line lil -ell of.

- Figure 9.

Figure 18 is air-elevation of a heat exchanger, portionsbeing brokena'wayto show the'interior. parts.

Figure 19 is ure l8.

Figure 20 is a plan view of a centrifugal p p with a driving motorattached thereto. I

Figure 21 is a sectional view on alarger scale a section on the linelfl-li of Figthe vertical eflects' shown Figure 8 is "a section'on theline Mb! Fig 10, but I the line oi j of a weir for condensate.

[Figures 1-3. illustrate a ten-effect evaporator containing theimprovements embodying the present invention. These ten eiiects areindicated as #I, #2,-#l'0, #i and #2 being as shown as vertical effects,#3 to it) being shown as horizontal effects. It is-evident that theinvention maybe embodied in multiple eiiect evaporators consisting ofdifferent numbers or vertical efl "ects, of horizontal eil'ects, anddifiering in the total number of e'flfects. The vertical and horizontaleiiects are more iullv illustrated in Figures 4 and 9 respectively,and'are hereinafter more fully described. In many respects, the...evaporator herein illustrated resembles that described andillustrated in my Patents Nos. 1,582,066 and 1,582,067. As shown, theeflects arearranged in order of descendingpressures and temperatures,effect #5 having the. highest temperature and pressure therein.

The apparatus illustrated on thedrawings is designed for. operation 'bysteam, high pressure .steam being supplied initially through a pipe .30I to the steam chamber of eiiect'it-i. Each of the effects hereindescribed consists of a boiler shell, the interior of which is dividedinto three chambers by transverse tube sheets, as hereinafter more fullydescribed. The intermediate cham-' her is the-steam chamber, a number oftubes being mounted in the tube sheets to extend through the steamchamber and to open into the two end chambers, These tubes carry theliquor to be evaporated; the liquor being heated by the steam in thesteam chamber. The liquor in the tubes is boiled as it passestherethrough so that-a mixture er steam and unevaporated liquorv isdischarged into one of the-end-chamhers. Theisteam is separated from theliquor and is carried over into-the steam chamber of a lowertemperature. This steam heats and boils the liquor passing through thetubes of this evaporator so' as to form steam. for operating; the nextsuccessive evaporator in a manner well 'known in the art of multipleefiect evaporation. As shown in Figures 1 and 2, the steam sepa- .ratedfrom the boiling liquor in #l eflect is sent through a steam pipe 3! tothe steam chamber of effect #2. The steam from #2- effect is 'sentthrough a steam pipe 32 to #3 effect. In like manner, the steam fromefl'ect #3 is sent through a steam pipe 33 to the steam chamber of,effect #i, and so on down the line until'the steam from #itl effectisdischarged through a steam pipe 3t to a condenser 35, diagrammaticallyindicated in'Figure 3. The steam lines to the successive horizontalefiects may be mechanically 'joined together to form an apparentlycontinuous pipe for the purpose of simplifying the supthe nextsuccessive evaporator which operatesat port thereof. j This pipe'isblanked 011 as at it between the supply line and end discharge line ofeach effect. If, for any reason, it is desired to out out an effectentirely iromthe apparatus, the corresponding blanking plate may beremoved so as to by-p'ass the steam past the efie ct thus cut out. Inheating the li or-in any of the eii'ects, the steam which enters theefiect is for the most part condensed sothat a consider-- pending on theeffect in which it is formed. In.

' able amount of condensate is formed in each ef-.

fect,-'the temperature of such condensate deorder to utilize the heat'in the condensate formed in the hotter effects, the condensate from eacheffect is sent successively. to the steam chambers of the remainder ofthe effects so that the excess heat .therein flashes of! into steam inthe successive steam chambers owing to the progressively lower pressurestherein, which helps to heat the liquor passing through the tubes. Thusthe condensate formed-in #I effect flows off through a pipe 40 to #2effect, this flow being controlled. by a suitable valve 4| ashereinafter explained in more detail. In like manner, the

condensate from veifect #2 flows of! through a pipe 42 controlled byasimilar valve 43, and is introduced into the steam chamber of effect #3.

The condensate piping system is illustrated more clearly in IJigure 3.As'shown, the pipe 42 extends continuously past all the horizontaleffects to a wzir 44, and thence downwardly to water-seal 4 which islocated thirty feet or more below the pipe 42 so that discharge may beaccomplished at all times therethrough at low pressures in-the steamchamber of #II effect without sucking air. At each effect a normallyclosed valve 46 is in the pipe line 42. On thesupply side of each valve46 a branch pipe 41 leads into the steam chamber of the correspondingeffect, or,. as shown, into the upper end of a well 48 which is mountedbelow the steam chamber of each effect to catch the condensate flowingtherefrom. The bottom of each well is connected as by a pipe 49 to theother side of the corresponding valve 46 so that when all the valves 46are in their normally closed position, the condensate flows upwardlythrough the branch pipes 41 and backthrough the 'wells 48 and connectingpipes 48 to the next section ofthe pipe 42. The pipes-41 and may besupplied with suitable normally opengate valves II and EL: If itisdesired to cut out any single effect from the series, theicorrespondingvalves 50 and 5| may be closed and the corresonding valve 46 opened soas to by-pass the condensate. The condensate from the condenser 35 isprefer-. ably sent through a weir t2 and down to a water-seal or trap 53located thirty feet or more below the condenser. V

Figure 3 also illustrates the piping system for removal of adventitiousair or other "gases which may be carried into .the effects with thesteam supply. It is practically impossible to supply steam which iswholly free from air or other gases. If such gases are allowed tocollect-in the effects, their pressure soon increases until it seriouslyaffects the operation of the effects, the

efficiency of which operation depends in large I measure upon thepressures maintained there= in. Hence, an exhaust pipe 55 is connectedto the upper portion of the steam chamber in #l effect and leads to .theupper: portion of the steam chamber-in #2 effect. From this steamchamber, a pipe 56 extends past all the hori- 'zontal effects to thecondenser 35. From the condenser a pipe 51 leads to a suitablevacuumpump, not shown. At each. horizontal effect, the

pipe 56 is stopped by .a normally closed gate valve .60. On either sideof these gate valvesare pipes iii, and 82 leading from the pipe 56 tothe upper portions of the steam chambers in the several effects. The airfrom #2 effect, together witha' certain amount of entrained steam,enters the steam charnber of #3 efiectthrough the pipe 6i The weakliquor which is supplied to the evap- 1o orator is preferably sent firstto-one of the intermediate eifects and thence through successivelycolder effects to effect Hi. from which it is sent through the remaininghotter effects in order of increasing temperature untilit is finallydischarged from effect #I, as described in my Patent No. 1,582,067. Asshown on the drawings by way of ilustration, the weak liquor isinitially entered in #5 effect. but it is apparent that it may beenteredfirst in any of the other eifects, as desired. As shown inFigures -1 and 2, the weak. liquor may be supplied from a storage tank14 through a supply line H which may be connc .ted with the tank 10 bothby a branch line l2'entering the tank at an intermediate point betweenits top and bottom and by another branch 13 entering thebottom of thetank. Suitable gate valves 14 and 15 may be supplied for controllingthese branch pipes. carrying hot weak liquor from the tank 10, isconnected to the suction end of a suitable pump 80 which dischargesthrough a pipe 8| into one of the intermediate effects, such as forexample, effect #5. through a heat exchanger 82 as illustrated in Figure1, for a purpose explained in my Patent N.o. 1,582,067 and hereinafterset forth. Each effect is provided with a supply pump Ill from whichliquor is pumped into the effect through a supply-pipe 8|. Theunevaporated liquor from 40 #8 effect is pumped into #6 effect. In likemanner, the unevaporated liquor from each of the 'next succeeding coolereffects is pumped from one effect to the next until the coldest effect#III is reached. The partially concentrated liquor from this effect issent through a pipe 85 to a pump #6 from.whichv it is discharged for themost part into a pipe 81 leading to theheat exchanger 82. This coldliquor,

'- in passing through the heat exchanger 82, receives considerable heatfrom the but weak r liquorv supplied from the tank 10 so that as itemerges from the exchanger '2 through a pipe 88, its temperature hasbeen considerably raised. Since the. pipe 28 leads to effect #4,.thehigher the temperature of the liquor-in this pipe, the

- less steam will be required in this effect to raise the liquor thereinto its boiling point. From the well 84 .of #4 effect. the unevaporatedportion of the liquor is discharged through a pump '24 to#! eifectandthence to the upper chamber of #2 eifect. From this effect,theunevaporated liquor is drawn oil from the lower chamber and is sentthrough a pump 80 to the upper chamber in- #l effect. The concentratedliquor from #I effect is finally discharged through a .pump, and a pipe88 to the furnace (not shown).

.For the proper operation of the evaporator as, a whole, it is necessarythat the flow of liquor. 70 through each'individual effect be carefullyregulated. so that there will be sufficient liquorsupplied to eacheffect, but not too much. In order to regulate such supply, a gate valve90 is mounted in the suction line of each pump 80, these (5 The pipe II,

This particular supply pipe 8| passes valves. being operated by; hand toadjust the evaporator as awhole to any particular condition,ofoperation. In addition to this regulation which takes care of sizeablechanges in the rate of supplyof weak liquor-to the evaporator and 'thetemperature of such liquor, I provide automatic means for taking careofsmall variations which occur constantly during the operatiomof theevaporatorand which arise from any one or more of-a considerable number.of causes. To this end, each of the pumps 00 is provided with a bypass9| through whichliquor discharged from any of the pumps 00 may bere-circulated' directly back .to the suction of the safmepump. In

each by-p'ass BI is a control valve 92, preferably of the butterflytype, as illustrated in Figure 23. The valves 92 are each automaticallyregulated,

in accordance with the level of the liquor in the well 80 of the eifectto which the liquor is' being pumped. Thus the rate of supply of liquorto any effect is controlled within a limited range by the liquid levelin the discharge well of the same effect. Hence, if any one of theeifects varies in its 'efliciency so as to evaporate a greater or lesspercentage of the hauler-supplied thereto so that the rate of supplychanges, this change.

in'the rate of supply afiects each-of the other effects; the supplystreams to these other efiects; being "individually regulated byrespective valves to; 02,-which in turn may be controlled by apparatussuch-as isillustrated in' Figure 22. As therein.

sh0wn, a float tank 93 may be-mounted alongside of each well 80, thetank being in'communicaftionwiththe well through a pair of connectingpipes 94 near the top and bottom thereof With- '11 I in'ithe tank is-afloat 95 of suitable size to which attached an endless chain 06 passingoyer a \-'pair .of sprocket wheels 01, 98. The lower sprocket wheel ismounted on. a shaft which '40 projects through the casing of the'floattank 93- and-which carries an external sprocket wheel 1-00. The latteris connected as by asuitable chain l0! to a larger sprocket wheel I01mounted on a' shaft I03, the butterfly member I00 of the I valve 02being also mounted on the shaft 803. .Since the liquid'level in thefloat tank 93 isalways equal to that in the well 8!, changes of levellathe well result-in a rise or fall of the float 00 betwe n: suitablelimit stops I05 and l 06.

This metres of the float rotatesthe external sprocket 'wh'eel 100, whichin turn turns the sprooketwheel I01- through the chain connection,

{0| and-thus varies theiangular position of the butterfly member. I04.11', for example, one of 65 the pump /i0; slows down so that it does not,draw

, flfth uricvaporated' liquor from the corresponding tothe well fromthat effect, the liquor ulate in the well, causing a rise of therein Thecorresponding rise .of level in the float, tank 93 raises the float 95and thus rotates thefsprocketwheel I02 through a pro- ,.tions.of fiber,scale, etc., than are other types 43, as shown in Figure 3A ,I'hesevalves are pref- I effect as fast as it is being .dis-

pumps are avoided. The butterfly type'of valve is especially desirablein this connection since it is less liable to become clogged by800111111118!- ofvalvesfl v Owing to the decreasing pressures in thesuccessive effects from #I to #10, it is not necessary to pump thecondensate formed'in the several effects from one to the next, thehigher pressures in the hotter effects being sufficient to force the 10condensate into the next successive eifects. Wherethe difference ofpressure between successive effects is moderate, I do away with controlvalves in the condensate pipe line by installing wells 48 of sufficientdepth to serve astraps beneath the steam chamber of each such effect. Intheoperation of a ten-effect evaporator. such as is illustrated on thedrawings, the pressure differences between successive horizontalefiects, are relatively small'so that the wells demoed-20 not beexcessively deep to provide suflicient liquidhead to prevent thepressure in these efiects from blowing steam through-the condensatepipes to the next eilects; On the contrary, the head of zontal'efiects.- Hence, in orderto keep instep with effects #3 to #l0, thepressure. difierences between effects .'#I and #2 and between effects #2and #3 must be considerably greater than the pressure diiferencesbetween successive horizontal efiects. For this reason, fit isimpracticable to attempt to provide wells suflicicntly deep between,effects #2 and #3 of suflicient depth to actas steam traps between theseefiects. ,Instead'I prefer to provide regulating valves, and I 40erably-of a non-clogging type suchas the butter--v fly valve illustratedin Figure 23. For the cone trol of'th'ese valves, I may provide floattanks H0 #whi'ch may be identlcal'in structure and asso-.

ciated mechanism with the float tanks 93 illus 4 5.

trated in Figure 22 and hereinbefore described" for the regulation ofby-pass streams in the liquor supply lines.

In concentrating'sulphate liquor 'by evaporation, the liquor eventuallyreaches a thick vis- 50 cous consistency which renders it ,exceedinglydiflicult to handler When theliquor has been concentrated to a-point atwhich or more thereof issolid material, it is so viscous that when coldit is an extremely tacky or gummy 55 solid, Hence, in order to pump suchliquor through p pes, it must be handled at relatively hightemperatures. For this reason, the liquor entering the evaporator isrouted first through the colder effects for partial concentration, then0 through successively hotter eifects until it is finally dischargedfrom the hottest end of the evaporator. Sulphate pulp liquors containcalcium salts which as a rule are more soluble in cold water than in hotwater so that there is an 1 increasing tendency on the part of theliquor as it becomes more concentrated and. hotter, to

spondihslylesser proportion of liquor passing force the calcium saltsoutof solutiomvboth by through the supply .pipe 8| into the effect;reason of the increased concentration and the Hence. the supply streamof liquor to' the effect is reduced until the supply'balancesthepreviously diminished dischargestream from th well 84. tByumea-nsofthese'by-passes for recircu ating a portion of 'the liquor dischargedfrom each creasing quantity of such' salt, is forced out of solution.into its solid form. :When first precipipump 80, undesirablebackpressures on the tatedfrom the solution, this salt is usually in its75 the scraper.

spider frame I31.

hydrated form (CaSO4. 2H2O) which .is soft solid. If this hydrated formof the salt is strongly heated, as by proximity to the heated surfacesof the evaporating tubes in the hotter effects, the water of hydrationis driven off with the formation of anhydrous calcium sulphate, known asanhydrite,

a hard glassy substance which" is exceedingly difficult to remove whenit forms as scale on the interior surfaces of heated pipes. According tothe present invention, I provide mechanism by which the formation-ofanhydrite is forestalled by scraping the hydrous calcium sulphate fromthe surfaces of the tubes in the hotter effects before it has a chanceto change into the anhydrous form. To this end, I may employ in thehottest effector effects, such as #I and #2 effects, scraping apparatussuch as is,illustrated in Figures 4-8. The effects in which scrapers areused are/preferably of the vertical type, each consisting of a verticalshell I I5 in which are mounted a pair pf tube sheets I I6 and III whichdivide the effect into three chambers, an upper chamber H8, anintermediate steam chamber H9, and a lower chamber I20. A plurality oftubes I2I extend through the steam chamber H9 from one tube sheet to theother and open into the end chambers H8 and I20 respectively. There isin the pipe I22, being supported by a flange I24 which rests on theupper end of the pipe I 22. Within each tube I2I is a hollow cylindricalscraping element I30, as shown in Figure '7. The upper and lower edgesof this scraper may be of suitable sharpness as indicated in the figure.This scraper is mounted-on the upper end of a rod I3I, the mountingbeing preferably a trifle loose so as to permit a slight wobbling of theaxis of To this end, each scraper element I30 may be provided with apair .of transverse plates I32 riveted or otherwise secured together.The ends of these plates are preferably welded as at I33 into lateralholes in the scraper element I30. Central portions of the plates I32 areshaped to receive a shaft or pin I34 at the upper end of the rod I3 I,the shaft. I34 being preferably threaded at its upper end to receive apair of nuts I35 which may be spot-welded after being screwed intoplace. This facilitates replacement of worn scraper elements I30. Thesupporting rods I3I are somewhat longer than the tubes I2I so that whenthe scraping elements I30 are near the upper ends of the tubes I 2| thelower ends of the rods I3I project downwardly below the lower ends ofthe tubes I2I a sufficient distance to reach a movable supportingplatform which may consist of a plate I35 mounted on a As shown inFigure 7, each supporting rod I3I may beprovided with a threaded lowerend portion I38 projecting through the supporting plate I36 and securedthereto as by a pair of nuts I40 which are preferably spot-welded afterbeing setup in position. The spider frame I31, as shown in Figure 6,

may comprise a suitable number of radiala'rms,

four such arms being shown, projecting from a central huh I. Throughthis hub projects the upper end portion of a shaft I42, the hub restingin my Patent No. 1,582,066.-

on a collar or flange I43 on this shaft. lln extension I44 of this shaftprojects upwardly through the central passage in the pipe I23,throughthe upper chamber H8 and out through the upper end of the shellH5, a suitable gland I45 being provided to-prevent the escape of steamfrom the chamber H8 to the atmosphere. The highly concentrated liquor in#I and #2 effects is of such a nature that it instantly becomes gummyupon exposure to air. Hence, in order to avoid excessive frictionalresistance of the I I5I fixed on the inner walls of the shell I I5 inthe lower chamber I20. In order to maintain true alignment of the spiderframe I31 and the scraper elements supported thereby, the shaft I42 isof-sufficient length to project through a slide bearing I52 set in thebottom of the shell H5. Projecting downwardly from the bearing I52 is awell I53 of sufficient length to receive the shaft I42 when the spiderframe I3! is inits lowermost position as indicated in dotted lines inFigure 4. A suitable by-pass I54 is provided between the lower end ofthe well I53 and the chamber I20 so as to permit displacement of theliquor in the well I53 when the shaft I42 descends thereinto, Aperforated baffle plate I55 may be provided adjacent to the lower end ofthe shell H5, the discharge pipe 89 being connected to the bottom of theshell below this baflie plate. During the operation of the evaporator,the pipes I2I are heated by high pressure steam which enters the chamberH9 through the steam supply pipe 30. This causes the liquor in the pipesI2 I to boil. The formation of bubbles in the columns ofliquor in thetubes I2I makes these columns of liquor lighter in weight. Hence, theliquid pressure immediately below the lower ends of these tubes, due tothe head of liquor in the large central pipe I23, is greater than thepressure of the columns of liquor in the tubes themselves. I2I areforced upwardly, the liquor flowing into the upper chamber I I8and'spilling back into the lower chamber I20 through the large centralpipe I23. The rate of heat transmission through the walls of the'tubcsto the liquor therein is limited, and depends partly on the velocity ofthe flow of liquor through the'tubes, .as explained There is acorresponding limit to the .rate of formation of bubbles in the columnsof' liquor in the tubes I2I.

practical'minimum the volume of liquor in each tube. To this end, Ipreferably make the su pporting rods I3I of comparatively large diameterso as to fill" a substantial portion of the space within each tube. Thisstructure increases the relative amount of-foam in the tubes and thusThus the columns of liquor in the tubes e,oao,oaa

into eim chambers m and us within the shell The speeding up of the'flowof liquor, in-the tubes I2I by displacing the liquor in the central oraxis portion of; thespace within the tubes.

serves to wash from the scrapers I30 the solids whichare scraped fromthe tube walls. It is evident that the extent of displacement of theliquor in. the central portion of the tubes depends not only on thediameter of the rods I3I but also on the position of the movablescraping apparatus including-the scrapers I30, the'rod I3I and the.

support I36, such displacement varying'periodically from a minimum, whenthe scraping apparatus is in its lowermost position, to a maximum whenthe scraping apparatus is in its uppeimost position.v Thus theupwardmovement of this apthe tubes HI.

paratus accelerates the flow'of liquor in the tubes I2I until a maximumvelocity of flow is reached when the scrapers are near the upper ends ofI This accelerated flow of liquoreffectively prevents any accumulationof solids on the scrapers min the upper portion of the tubes. 1

Any suitable apparatus for reciprocating the scraping mechanism maybe'employed. In Figure 1 there is illustrated mechanism for thispurpose. The upper ends of the shafts I44 are preferably attached tosuitable cables I60 which carry oounterweights-'(not. shown) to take thedeadweight load. of the scrapers and their supporting members from the 4ing these members. Asshown, the upper portion of each shaft I44 isscrew-threaded for ,a considerable length as at I BI, this threadedportion surfaces thereof.

being in threaded engagement with a nut I62 on which is mounted a wormgear I63 meshing with a worm I64 which may be driven by a suitable motorI65.- Since the shaft I44 is prevented from rotation onits axis by theguides I5I ahd a key inserted in the bearing in engagement witha keywayin the part of the shaft having a screw thread, rotation of the wormshaft I44 to rise or fall-according to the direction of rotation of theworm gear. Suitable automatic controls (not shown) are provided toreaches either end of its stroke, means being well known in the art. Forthe lubrication of the threaded-portion I may provide an oil reservoirthe lower end of the threaded portion: Oil which collects. in thisreservoir maybe pumped by a small motor "I through a flexible hose I72to be discharged through .a suitable nozzle I'll on the threaded endportion IIiLimmediately above the nut I62; .The motor I65maybe-operatewat any desired rate to ensure sufficiently frequentscraping of the inner surfaces of the tubes I2I- to'prevent the depositFigure 9; of the drawings illustrates in longitudinal section oneof thehorizontal eflects employed in the evaporator." As. shown, each suchare'mounteda pair of'tube' sheets I8I, I02. A number of horizontal tubesI83 extend. from the mechanism for mov- I6 I of the shaft, I10 mountedat of anhydrite scale on the inner I; In large sized efl'ects. the tubesI83 may be of-oonsiderable length so that'I may provide one or moreintermediate tube sheets I86 to supintermediate steam chamber I81 intotwo or more compartments, such compartments. being in communication=witheaoh other as by an,opem'ng I I88-formed by cutting away the lowerportion of each intermediate tube sheet I86. This permits 10 free flowbfcondensate from the various portions of thesteam chamber into the well48. Step arate steam inlets. I00 and I9I are preferably provided for theseveral compartments of "the steani chamber so as to ensure a suflicientsu'p- 15 ply of steamto all the exterior surfaces of the tubes I03. Theliquor to be evaporated is sup: plied through one or more pipes. 8| froma supply pump 80, which enter the supplychamber. I84. The volume rate ofdelivery of weak liquor tothe evaporator is subject to considerablevariation at times owing to conditions of'operatio'n in the pulp mill.There is a practical limit tothe size of anozzle of the type describedin my Patent No. 1,582,066 for effective breaking up of the jet 25 ofliquor supplied at various pressures, into a uniformlydistributed sprayfor projection against the tube sheet I8I and the open ends of the tubesI83 projecting therethrough. Hence, in order Q1) provide ample supplycapacity for each effect; 30 may employ a battery of spray nozzles I92,each such nozzle being of suihciently small size to be effective inuniformly distributing the liquor flowing therethrough regardless of thepressure' at which the liquoris supplied. The lower nozzles 35- arepreferably of somewhat smaller diameter than the larger nozzles tocompensate for differences f in liquid pressure due to 'liquid-head. Bythis gear I63 will causeythe means, a substantially uniform distributionof liquor over the face of the tube sheet IBI may be 40 obtainech. It-issometimes necessary to operate the evaporator under radicallydifferentconditions of liquor supply. In order to take care of thisproblem, I may provide two batteries of nozzles as'indicated'in'Figure10. Figure 11 illus- 115 trates onesuch battery of nozzles, thesenozzlesbeing mounted on a manifold I93 of piping so as to support the nozzlesin a symmetrical array for uniform distribution of liquor therefrom. Ina'Q- dition to the manifold I93 I may provide a sec- 50 ond manifoldI94, each manifold being controlled by a separate gate valveso thateither one may reverse the motion of each shaft I44 when it suchreversing.

eflect consists of'a boiler shell I00-within 'which tube sheet III "tothe tube. sheet m an open surfaces to'the liquorc be shut off entirelywhen not needed. By this means, the supply rate'of liquor to'anyhorizontal effect may be radically changed without neces- 65 sitatingaccessto the interior of the chamber I84 ,for the purpose ofchangingmozzlesy As described and-illustrated in my patents here-.inbefore referred to,'.a series of gill flanges I95 may bemounted on theface of the tube sheet 60 I8I to assist in the uniform distribution ofliquor projected against the tube sheet. into the several horizontalrowsof tubes, orie such flange I95 be'- ing mounted beneath the orificesof 'each such horizontal row oftubes. I 7 tion of the .efiects; it isnecessary that 'the entire inner surfaces of all the'tubes I83 beconstantly wetted by llquonso that there will be anuninterruptedtransfer of heat from all the heatin of liqu'or to aneifeothas beeninsufllcient to keep the I83 sumciently filled with liquorto wet theentire interion'surfaoes thereof, it-has been my previous practice torecirculate a portion of liquor from such effect to the sup- 75 When thesupply stream 7 port such tubes. These sheets may divide the 5 Ferv the'efiicientopera- .65

according 'to the present invention, other means for maintaining asuflicient supply of liquor in the tubes I00. To this end, I providedams or bar-'- riers outside of the discharge ends of the tubes I03,these dams being preferably in the form of transverse plates secured tothe tube sheet I82, the lips of these plates being approximately on alevel with the central axes of the tubes in the corresponding horizontalrow, as illustrated in Figures 14 and 15. These dams may be of anysuitable shape, having a vertically extending wall I as shown in Figure14, or an outwardly sloping wall I" asshown-in Figure 15 Dams of thiskind back up sufliclent liquor in the tubes I03 to ensure thoroughwetting of all the interior surfaces of these tubes by the'boiling andresultant foaming of the liquor therein.

In the ordinary operation of a horizontal effect of the type illustratedin Figure 9, the liquor in the tubes I00 rushes through the tubes withconsiderable velocity owing to the ebullition of the liquor therein and.the difference of pressures in the end chambers of the effect. Thisvelocity of the liquor'within the tubes makes for eflicient heattransfer from the inner tube surfaces to the liquor itself. One resultof this velocity and foaming of the liquor'is the delivery of a mixtureof finely divided liquor and steam in large quan- This chamber servestitles into the chamber I00. as a separation chamber in which the steamis separated from the liquor, the-steam being discharged upwardlythrough the connection 30 to the section of the steam line 02 throughwhich it is delivered into the steam chamber of the next adjacenteffect. Since'this steam is condensed in the next eflect In the courseof heating and boiling the liquor in the tubes oi! the next effect, thecondensate therefrom is delivered into the well 00 of the next eifectand follows the course of the condensate through the several wells 08 tothe weir 44 and the trap 45, as hereinbefore described. It is evidentthat if by escape of the condensate. -Hence it is important that theseparation of steam from liquor in the chamber I00 be as complete aspossible.

'This separation is made difllcuit by the delivery of large quantitiesof foam and finely divided liquor from the tubes I00, and by the highvelocities of the streams of steam flowing from the effects,-particularly in the case'of the low pressure 'eifects where the volumeof the steam is greatly magnified, by the low pressures. In order toobtain an efllcient separationof steam from liquor, a baiile plate "I ismounted in the chamlllsloping downwardly away from the tube sheet I02.Considerable clearance is allowed be I, w I v 'thence 'upwardlythrough-the outlet 200.

2,020,088 ply endof the same eflect so as to maintain a tween the loweredge of this plate and the bottom of the shell I00 80 as to provide anample passageifor the steam to escape to the portion of the chamberbeyond, the baflle plate MI and cording to the presentinvention, I formthe lower edge 202 of the baiile plate 20l in such a manner as to slopedownwardly from a high central point.

' Along the greater portion of this edge on the side of the baille platetoward the tube sheet I82, I 10 mount a suitable gutter 203. Thisgutteris of suflicient size to accommodate the liquor which strikes the faceof the plate MI and runs down thereon toward the lower edge. The gutterthus prevents the formation of a curtain of liquor dripping from thelower edge 202 of the baflle plate I and thus avoids a tendency on thepart of the stream of steam flowing through the opening beneath thebaflle plate to sweep such drippings of liquor upwardly through thechamber 20 I85 and the outlet 200 into the steam chamber of the nexteflect. The gutter 203 leads such liquor laterally to the sides of theshell I00 so that it flowsdirectly into the well 00.

As shown in Figure 16, I may provide within A the steam chamber I01 ofeach horizontal eflect a longitudinally extending baiile plate 205 whichprojects downwardly from the upper portion of the shell I00 to a pointwll above the lower portion of the shell so as to provide ampleclearance between the lower edge of the baflle and theinner surface 'ofthe shell. This bafile plate is preferably mounted-oili to one slple' asubstantial distance from the median plane of the effect. As

shown in Figure 16, it is placed to the right of themedian plane. Theair pipe connection 6| from theprvious effect enters the upper part ofthe steam chamber-on one side of the baffle plate 205, the air dischargepipe 02 being. connected to the steam chamber on the opposite 4 side ofthe plate 205. As shown, the baifle plate may be adjacent to the orificeof the discharge pipe 6;. During the operation ofthe evaporator, thereis a constant suction maintained on the air line so as to create aflowthrough the con- 5 necting pipes 0| and 02 from. one eiiect to theother along the line. Any air or other gases which may be present in anyof the effects is projected downwardly from the pipe BI into the steamchamber I01 together with considerable o entrained steam.-- The suctionin the pipe 62 draws such air over to the adjacent side of the, steamchamber so that the air is more efllc iently removed from thesteamchamber than it can be when the inrush of steam through the inlets I90to be condensed on the tubes I03 tends to sweep such air or gasesdownwardly to the bottom of the effect. The bathe plate 205 thus resultsin a more efllcient removal of adventitious air from the steam chambersof the several ef- 5 fects, with a consequent improvement in theeiliciency of the evaporator as a whole.

As hereinbefore stated, a primary object of the evaporator is to recoverthe chemicals in the weak liquor so that it is desirable that none ofthese 55 chemicals be lost with the condensate from the steam suppliedto the various effects. In the -average mill, the operators work more byrule of thumb-than according to actual knowledge of what is going oninside of the apparatus. Hence 7 it is desirable that means be providedfor checking up on the functioning of the evaporator to see that-suchlosses'ofliquor containing valuable chemicals are notoccurring. Forexample, an operator may be instructed to carry 28 Inches of vacuum inthecondenser. If the barometer reads 29 inches of atmospheric pressure,that will mean that if a 28-inch.- vacuum is maintained in the sure of 2inches.

of the low pressure effects, excessive vacuum in the condenser mayresult in the entrainment of more or less liquor in the steam. Such'apossibity is avoided as far as is practical by designing the apparatuswith'large steam delivery pipes 33 which increase in size for theeffects operating at lower pressures, as indicated in Figure 1, so as toreduce the steam velocities by large cross sectional areas of the pipeswhich carry the steam from the low pressure effects. In any actualinstallation, however, there are "limits to the steam velocities whichcannot-be exceeded without carrying more or less liquor into thecondenpercentage of liquor in' the condensate colors it so thatit caneasily be detected. To this end; I

may employ .weirs such as that illustrated in Figure 24. As shown, thisweir consists of a container 2l0 having a'transverse wall 2, forming aninlet chamber H2. The wall, 2 is suitably notched as at 2|! to permit aflow of liquid from the chamber M2 to the adjoining chamber 2l4. Thelevel of the liquid in the chamber 2l2 is a i'unction of the rate ofsupply of the liquid to the chamber, this rate being indicated by asuitable scale'2l5 opposite a sight glass 2; through which the level maybe observed. The condensate is supplied to the chamber 2I2- through asuitable pipe 211. In the chamber 2 is a dam 220, the

'crest of which is lower than the bottom .of the notch 2 IS. The liquidflowing over the crest of the dam 220 escapes through a discharge pipe22L A sight glass 222' is mounted in an inclined position outside of thecontainer 210, the lower end of the glass, communicating with th'e'pool'of liquid behind the dam 220, the upper end of the glass opening into.thechamber 2 l4 in front'of the darn 220 and below its crest so thatthere is a constant flow of a portion of the pool behind the dam 220through the sight glass 222. This glass ifproperly illuminated,indicates the purity of the condensate delivered to'the weir, thepresence of any appreciable percentage of liquor visibly discoloring thecondensate flowing therethrough. Thus if any liquor is being lost byentrainment in one orv more 'streams'of steamfrom the eifects, its

presence is readily observable, and the evaporator can be accordinglyregulated .to avoid suchescape of liquor.

lf'Theheat semisy which a hot weak liquor ismadetogivehpa portion 'ofits heat to warm the coldliquor passing from #I'O effect to i #4 meet'is-preferably gfconsiderable length m order to as much heat as possiblefrom the weak' liquortto'tne partially concentrated aoaqoae 1 1' liquor.In order to-avoid danger of clogging in elbows or 'bends, such heatexchanger-is preferably constructed in'a single extended length, asindicated in Figure 1,- the actual length of the exchanger employed inthe apparatus illustrated 5 being approximately sixty feet. Since it isim practicable to employ tubes of such length, I prfer to build the heatexchanger in sections as indicated in Figures 18 and '19. As shown, the

heat exchanger may comprise three sections, but 0 it is apparent that agreater or lesser number of sections may be employed in like manner.The. heat exchanger, as shown, consists of two end sections with orwithout one or more intermediate sections. Each end-section consists ofa shell 230 15 with an end plate 231 and a tube sheet 232 adjacentthereto forming an end chamber 233. At the oppositeend of this sectionis a second tube sheet 234. A number of tubes 235 extend between and.open through the tube sheets 232 and 234: The 20 outer face of the tubesheet 234 is preferably ground or otherwise made truly plane so as toabut a similar tube sheet forming an end of the adjacent section of theheat exchanger. If intermediatesections are employed, one suchintermediate section being shown in Figure 18, both ends of suchintermediate section consist of tube sheets 234adapted to abut theterminal tube sheets of the adjoining end sections. Each of the' tubesheets 234 is formed with an'identical pattern of perforations, such asthat shown in Figure 19, so that the perforations of pairs of abuttingtube sheets 234 register; with each other. In addition to theperforations to receive the tubes 235, the tube sheets 234 areadditionally perforated between the tubes 235 as at 236. Since thecombined areas'of the openings 236 are neces sarily considerably smallerthan the cross sectional area of the spaces between the tubes 235 withinthe shell 230, I preferably provide addi- 40 ticnal apertures 281 oflarger size through the' tube sheets 234, as shownin Figure 18. In orderto provide such apertures, one or more of the tubes 235 must be omitted."The omission of these tubes moreover servesthe purpose of providingdistribution chambers 24!! adjacent to the orifices of the supply pipes8| so that the entrance 'of liquor into the inter-tubular space withinthe shell 230 is not impeded by the presence of pipes 23!! directly infront of such orifices. For the efficient functioning of the heatexchanger, it is necessary that the liquor flowing through theinter-tubular spaces be distributed in these spaces as uniformly aspossiblev so as to maintain asun-ifor'm atemperature gradient aspossible from one end of the exchanger to the other. Since the omissionof one or more tubes 235 would provide easy channels for the flow ofliquor from the chambers 240 to the openings 2-31 without touching thetubes, which would reduce the 'eifectiveness of the exchanger, provisionis made to close oil. such channels by the location of' volume-occupyingmembers 2 therein. These members may be in the form of ,pipes'ofsuitable size, closed at the ends, and mounted on the walls of the shell2" in sucha manner as to fill most got the space between the chambers240 and theopenings 231, clearance being allowed adjacent tothe latter,as at 242, to facilitate the flow of liquor to and from theinter-tubular openings 281. a

" 'The pumping of liquor from one effect to another has heretofore beenattended by difiiculties owing to the fact that the unevaporated liquorleaves each elect at a' temperature very close to 76 spaces through the7 I carries the paddleswheel.

its boiling point so that if any appreciable heat is added thereto,steam tends to form therein. Pumps arenecessary for the proper transferof liquor from one effect to another. No pump is perfectly efficientmechanically, that is, in any pump there, is necessarily a generation ofheat duetofriction such as between the pump parts and the liquor.troublesome steam in the pump which seriously affects the operationthereof. It has been found as a practical matter that the centrifugaltype of pump is best suited for the transfer of liquor from one effectto another. The generation of heat within a pump of this kind tends toresult in the formation of a steam pocket within the casing of the pumpwhich holds the liquor away from the paddles and thus interferes withthe pumping action. It would be undesirable and ineflicient to attemptto chill the entire liquor stream supplied to these pumps sufficientlyto prevent such formation of steam. Various expedients, such as mountingthe pumps in deep pits so that the pumps operate at least thirty feetbelow the bottom of the effects, have been tried withmore or lesssuccess, such expedients being in general open to practical objectionssince the pumps must be readily accessible if they are to receivenecessary care and attention. According to the present invention, Iprovide simple but effective means for preventing objectionableformation of steam pockets in the pumps by supplying thereto cold liquoralong the surface of the shaft which By introducing a cold liquid inthis manner at the center of the pump casing, a relatively smallquantity is amply sufficient to condense the steam in the pump casing orto prevent the formation of steam in objection able amounts therein,without unduly chilling the stream of liquor as a whole. Furthermore, byemploying cold liquor-irom #ill effect, there is no loss of. efficiencyin evaporation since the water contained in this partially concentrated60. As shown in Figure 20, the liquo'r'supply pipe on the suction sideof the pump enters the suitable motor 253 or other convenient means ofpump casing through one side thereof, the paddle within the pump beingmountedon a shaft 252 which enters the opposite side of casing and ispreferably aligned with the supply orifice. A

driving the shaft 252 is connected-thereto. According to the invention,the shaft 252. extends through a, hollow boss-254 which projectslaterally from and may be integral with the side of the pump casing 255.The boss 254 has an interior bore of sufllclent diameter to form aninterior shoulder 256 with the casing wall 255 but to leave The heatthus generated results in shaft. This .clearance is carefully regulatedso as to provide a passage of definite cross sectional area between thechamber 26 I and the interior of the pump casing. The branch pipe icommunicates with the chamber 26I by suitablev passages in the member260. To this end, the memher 260 may be provided with an exteriorperipheral groove 263 communicating with thechamber 26f through one ormore apertures 264. Between the outer end of the member260 and gland 265is a suitable packing 265 to prevent the escape of liquid from the pumpcasing along the shaft 252. The cold liquor supplied from #IO effectenters in a small stream through the pipe 25! and the passages in themember 260, including the clearance space 262 about the shaft, so thatthe cold liquor reaches the center of the pump casing -along the surfaceof the shaft, precisely where y it is most effective. This continuoustrickle of cold liquor into the center ofthe pump efiec- 20 tivelyprevents the formation of objectionable steam pockets therein. In orderto avoid the necessity of control valves for regulating the size of thestreams of cold liquor into the pump J -avoidable, I employ the members260 for such regulation. If a larger or smaller rate of supply of coldliquor to any pump is desired, the memper 265 may be quickly and easilyreplaced by a similar member having a larger or smaller clear- 30 once262.

One of the problems of pulp mill practice arises from the veryconsiderable loss of heat energy due to the escape of large quantitiesof steam when a digester is discharged into" the blow pit.

According to the present invention, I avoid a great deal of such loss byutilizing blow-pit steam and any'other steam available in the mill whichwould otherwise be wasted, by sending such steam through a suitable pipe280 into a condenser 26I 40 of suitable size and construction. The steamsupplied .to this condenser condenses on the surface of a number oftubes therein which are full ofweak liquor circulated from the storagevat l0.

. As shown, a supply pipe 282 may lead from the bottom of the vat to thecondenser 28l, a return pipe 263 leading from the condenser back to thevat 10 at a point considerably above the bottom ,of the vat, butpreferably below the average working level of the liquor stored .n thevat. The heat given up by the condensation of the steam in the condenser26I serves to raise the tem:- perature of the liquor within the tubes ofthe condenser. Whether or not the liquor is thereby boiled, its specificgravity will be lowered so that there will be a natural gravitationalcirculation of liquor through the condenser from the bottom of the vatto the point of entry of the return pipe 263. If desired, a suitablepump (not shown) may be employed to assist circulation.

a considerable clearance 25'! between the shaft It is obvious'that thehotter the liquor is when and the wall 255. Within the bore 'of the boss25; I insert a gland member 260, this member being adapted to engagewith its inner end against the shoulder 256. The member 260 is in thegeneral shape of a hollow cylinder having a central bore adapted toreceive the shaft 252. The central portion of the bore is relieved orenlarged as'at 26! to form a chamber around a portion of the shaft 252.The inner end of the bore-is also slightly larger in diameter than theshaft 252 so as to provide a definite clearance 2621about the casing,the use of valves being objectionable ,where 25.

locity offlow over said surface during each period I of .scrapingmovement in'said direction.

2..In the art of evaporation, a processjwhich comprises flowing liquorover a heated surface, periodically moving a scraping element acrosssaid surface at substantially constant speed in the direction of flow,and continually incre ing the velocity' of flow over said surfaced eachperiod of scrapingmovemen't in said direction.

3. In the art of evaporation, a process which comprises flowing liquorover a heated surface,

, intermittently scraping said surface, during said flow with a movementin the direction of flowand slower than the flow itself, andcontinuously increasing the velocity of flow during each period ofscraping movement in said direction.

4. In the art of evaporation, a process which comprises flowingliquonovera heated surface,

- motion in the direction of flow.

scraping said surface during said flow by alternate through said tube,scraping the inner surface of,

said tube from end to end-altemately withand against the flow andprogressively displacingliquor from the central portion of the spacewithin the tube during the scraping movement in the direction offlow.

'6. A process of evaporation, which comprises delivering liquor into anexternally heated horizontal tube and maintaining the quantity ofliquorin said tube above a predetermined minimum by backing up a portion ofthe liquor in the tube froma point beyond the, discharge end thereof,whereby the interior of said tube is unobstructed.

7. In the art of multiple-effect evaporation, the. method offacilitating the centrifugal pumping of liquor at its boiling point fromone effect to an-- other, which comprises injecting into the centrifugalchamber a small stream of cold liquor of high- 'est unit through saidheat-exchanger to the super concentration. F

8. In the art ofmultiple-efllect evaporation, a process which;.comprises supplying weak liquor initially to an intermediate effect,pumping the liquor from each effect to the next effect at a temperaturenear its boiling point, concentrating said liquor by steps insuccessively cooler effects to the coldest effect, then through theremaining effects at successively higher temperatures to the hottesteffect, and introducing a portion of the partially concentrated liquorfrom the coldest effect into the pumping chambers of the several liquorpumps to counteract steam-forming tendencies therein.

9. A multiple-effect evaporator comprising a series of combinedevaporating and condensing units adapted to operateat descendingtemperatures and pressures, each said eflect having a supply port forthe'introduction of liquor to be concentrated therein, a heat exchanger,a supply line for initially hot, weak liquor leading through saidexchanger to the supply port of an intermediate unit, connectionsbetween said intermediate unit and the cooler units for conductingliquor through said cooler units in series for concentration therein, apipe line for liquor extending from the coldply port ofth unit nexthotter than said intermediate.- unit, connections for conducting liquorfrom said next hotter unit through the 2,020,038 of said flow, andcontinuouslyincreasing the .ve-

upwardly therefrom.

units in progressively hotter sequence, pumps said liquor connections;and means for conducting small streams of liquor from the coldest unitto the pumping chambers of the several pumps to counteract steamforming'tendencies therein. 5

' 10. In an evaporator unit of the vertical type, a boiler shell, a pairof horizontal tube sheets therein, vertical tubes opening through saidsheets, a frame vertically reciprocable in said shell below the lowertube sheet, stems mounted on said frame projecting upwardly into theseveral tubes, a scraper element at the upper end of each said stem, 2.central guide shaft projecting downwardly from said frame, a guidebearing fixed in the lower end of said shell, a fluid-tight wellextending down 15 from said bearing to receive said shaft, and means Ifor reciprocating said frame and scrapers.

11. In an evaporator wit, a vertical tube for liquor, a hollow scraperreciprocable in said tube, a hollow stem projecting into said tube andcar- 20 rying said scraper, said stem having a cross-sectional areaequal to a substantial fraction of that of the interior of the tube, andmeans for reciprocating said scraper in said tube from end to endthereof during the operation of said unit.

12. In an evaporator unit, a vertical tube for liquor, a hollowcylindrical scraper loosely fitted in said tube and reciprocabletherein, a stem carrying said scraper at one end thereof, said stembeing hollow for most of its length and having a 30 cross' -sectionalarea equal to' a substantial fraction of that of the interior of thetube, and means for reciprocating said scraper in said tube from end toend thereof. r i 4 13. In an-evaporator unit of the vertical type in- 5cluding a boiler shell and tubes therein for liquor, scraping mechanismfor the tubes reciprocable in said shell, means for reciprocating saidmechanism including a rod projecting through the top of said shell,a'gland on -said shell for said rod, and 0 means for maintaining apoolof liquid about said gland and adjacent portion of therod projecting 14.In an evaporator unit having a tube sheet and a set of horizontal tubesopening through, said 45 sheet, a battery of spray nozzles directedtoward said' sheet and. open tube ends and laterally spaced from eachother to spray liquor substantially uniformly over the face of saidsheet, an

. auxiliary 'batteryo'f nozzles spaced between the 50;

first said nozzles, supply pipe lines to said batteries, and valves insaid supply lines.

15. An evaporator unit comprising a pair of tube sheets, a plurality ofrows of substantially horizontal tubes'extending between andopeningthrough said sheets, means for supporting said sheets for theapplication of heat to the exterior surfaces of said tubes, meansopposite one of said sheets for distributingrliquor in the form ofsprayv thereagainst and intov said tubes, and means andpipes extendingthrough said chamber to conduct liquor for evaporation byiconden'sationof steam on the exterior. surfaces of said'pipes, a well under eachsteamchamberto receive condensate-therefrom, anda connecting pipe fromthe bottom of said well to the chamber of the next, successive eiiect,said pipe having a portion at a level suiiiciently below said eflect tobe kept full of condensate by the liquid head therein opposed to thediilerence of pressures inthe steam chambers of said effects with whichsaid pipe communicates] g 1'7. In a multiple-eiIect evaporator, aplurality of effects in series, a pipe line for transferring liquor ator near its boiling point from one effect to another, a pump in saidpipe line, and means for introducing a stream of cold liquor from one ofsaid eiIects into .the pumping chamber of said pump during the operationthereof to prevent the formation of steam therein.

18. In a multiple-eitect evaporator, a plurality for conductingunevaporated liquor from said intermediate eiIect to successively coldereiIects and from the coldest eflect to the remaining effects in sequenceof ascending temperatures, a pump aoaopsa in each said pipe connection,and means for diverting a sumcient portion of the partially concentratedliquor from the coldest effect to the pumping'chambers of certain ofsaid pumps to prevent said pumps from becoming steam-bound.

20. In a multiple-eflect evaporator, a series oi effects", pipe linesfrom one effect to another arranged to conduct the liquor from effect toeiIect in a predetermined order such that the liquor leaving the coldesteffect is partially concentrated, a centrifugal pump in each said pipeline, means including a rotatable shaft for driving said pump, fluidconnections from the pipe line leaving the coldest eiIect to certain ofsaid pumps, and means for introducing cold liquor through each saidconnection into the pumping chamber of the corresponding pump along thesurface of its driveshaft.

21. In amultiple-eflect evaporator, a condenser, a steam pipe leadingfrom the coldest effect to said condenser, a drain pipe from saidcondenser to lead of! condensate therefrom, a weir connected in saiddrain pipe, and means associated with said weir for indicating the rateof flow of condensate therethrouzh and transparent means through which aportion of the stream of condensate is by-passed to facilitate detectionoi. color changes therein.

HUGH K. MOORE.

